A conventional power conversion apparatus includes an inverter, a high-frequency transformer, and a bidirectional switch, and rectifies, by the bidirectional switch, a positive-and-negative square wave pulse train stepped up by the high-frequency transformer, into a square wave pulse train having a single polarity. Two or more series circuits such as a series circuit composed of a power switch device AS1 and a capacitor C1 and a series circuit composed of a power switch device AS2 and a capacitor C2 connected in a direction opposite to the first one, are connected between both output-side ends of the high-frequency transformer. The power switch devices AS1 and AS2 operate in synchronization with the polarity of output voltage of the high-frequency transformer, thereby clamping surge voltage caused on the output voltage of the transformer, at the voltage of a capacitor C1 or C2 (for example, see Patent Document 1).